The present invention is generally directed toward spiral wound modules. Spiral wound modules (also referred to as spiral wound “elements”) are well known for use in a variety of fluid separations including both gas and liquid phase separations. Due to their spiral configuration, a relatively large membrane surface area can be packed into an individual module. Depending upon the type of membrane utilized, spiral wound modules can be used in a wide variety of applications including: reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF) and microfiltration (MF). A typical module comprises at least one membrane sheet wrapped about a permeate collection tube. Examples of such modules are described in U.S. Pat. No. 5,114,582; U.S. Pat. No. 5,538,642; and U.S. Pat. No. 5,681,467. Such modules commonly include feed spacer sheets to facilitate flow of feed fluid thru the module, as described in U.S. Pat. No. 6,881,336. In use, multiple modules may be interconnected by way of end caps as described in U.S. Pat. No. 6,632,356, with multiple modules housed within a common pressure vessel as described in US 2007/0272628. Alternatively, a single module may be utilized as described in U.S. Pat. No. 6,066,254 and U.S. Pat. No. 6,299,772.
Composite membrane sheets are commonly used in spiral wound modules. Examples include FilmTec Corporation's FT-30™ membrane—a porous polysulfone sheet including a thin film polyamide discriminating layer formed by an interfacial polycondensation reaction between a polyfunctional amine monomer and a polyfunctional acyl halide monomer. Representative examples of such membranes are described in U.S. Pat. No. 4,277,344; U.S. Pat. No. 6,878,278; and US 2008/0185332.
An alternative type of membrane sheet includes a porous structure including integral capillary channels as described in U.S. Pat. No. 5,046,936; U.S. Pat. No. 5,089,187; U.S. Pat. No. 5,171,493; U.S. Pat. No. 6,787,216 and US 2009/0011182. Such membranes may be extruded from a polymer mixture (e.g. polysulfone, polyether sulfone, polyvinylidene fluoride) into a porous sheet including a plurality of parallel aligned capillary channels. U.S. Pat. No. 6,787,216; JP 59-82906 and FR 2,616,812 further describe the use of such membrane sheets within spiral wound modules wherein the capillary channels serve as feed fluid pathways. WO1981/002750 describes the manufacture and use of similar membrane sheets in connection with dialyzers.